Light-emitting device

ABSTRACT

Disclosed is a light-emitting device ( 1 ) including a light-emitting element ( 2 ) emitting primary light, and a light converter ( 3 ) absorbing a part of the primary light emitted from the light-emitting element ( 2 ) and emitting secondary light having a longer wavelength than the primary light. The light converter ( 3 ) contains a green light-emitting phosphor ( 4 ) and a red light-emitting phosphor ( 5 ). The green light-emitting phosphor ( 4 ) is composed of at least one phosphor selected from a divalent europium-activated oxynitride phosphor substantially represented by the following formula: Eu a Si b Al c O d N e  and a divalent europium-activated silicate phosphor substantially represented by the following formula: 2(Ba 1-f-g MI f Eu g )O.SiO 2 , while the red light-emitting phosphor ( 5 ) is composed of at least one phosphor selected from tetravalent manganese-activated fluoro-tetravalent metalate phosphors substantially represented by the following formulae: MII 2 (MIII 1-h Mn h )F 6  and/or MIV(MIII 1-h Mn h )F 6 . Consequently, the light-emitting device ( 1 ) has excellent color gamut (NTSC ratio).

This application is continuation of U.S. patent application Ser. No.13/542,051, filed Jul. 5, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/920,516, filed Sep. 1, 2010, which is the U.S.national phase of International Application No. PCT/JP2009/052051 filedFeb. 6, 2009, which claims priority to Japanese Application No.Application No. 2008-052210 filed Mar. 3, 2008, the entire contents ofeach of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light-emitting device including alight-emitting element emitting primary light, and a light converterabsorbing a part of the primary light emitted from the light-emittingelement and emitting secondary light having a longer wavelength than theprimary light.

BACKGROUND ART

A light-emitting device having a combination of a semiconductorlight-emitting element and a phosphor attracts attention as anext-generation light-emitting device where low energy consumption,compact size, high brightness and wide color gamut are expected, and isactively researched and developed. As the primary light emitted from alight-emitting element, the light having a wavelength in a longwavelength UV to blue region, namely, 380 to 480 nm is usually used.Also proposed is a light converter using various phosphors suited forthis application.

Further, in recent years, development of a backlight for a small-sizedliquid crystal display (hereinafter, LCD (Liquid Crystal Display))becomes more competitive. In this field, various methods are proposed,however, a method satisfying both brightness and color gamut (NTSCratio) has not been found yet.

Currently, as a white light-emitting device, a combination of a bluelight-emitting element (peak wavelength: about 450 nm), and a (Y,Gd)₃(Al, Ga)₅O₁₂ phosphor activated with trivalent cerium that isexcited by the blue light and exhibits yellow light emission or a(Sr,Ba,Ca)₂SiO₄ phosphor activated with divalent europium is mainlyused. However, in such a light-emitting device, color gamut (NTSC ratio)is about 65% (CIE 1931). On the other hand, in recent years, even in asmall-sized LCD, more excellent color gamut is demanded. Under such abackground, it is an urgent need to improve the color gamut (NTSC ratio)of a backlight for a small-sized LCD.

For example, Japanese Patent Laying-Open No. 2003-121838 (Patentdocument 1) focuses on color gamut (NTSC ratio) in LCD. Patent document1 describes that a backlight light source has a spectrum peak within therange of 505 to 535 nm, and an activator of a green phosphor used forthe light source contains either europium, tungsten, tin, antimony ormanganese, and also describes that MgGa₂O₄:Mn, Zn₂SiO₄:Mn is used as agreen phosphor in an example. However, when the peak wavelength of thelight-emitting element falls within the range of 430 to 480 nm, thephosphor containing either europium, tungsten, tin, antimony ormanganese is not entirely applied. More specifically, in the MgGa₂O₄:Mn,Zn₂SiO₄:Mn described in the example of Patent document 1, its luminousefficiency is significantly low with excitation light ranging from 430to 480 nm.

Further, for example, Japanese Patent Laying-Open No. 2004-287323(Patent document 2) describes, in addition to a RGB-LED where a red LEDchip, a green LED chip and a blue LED chip form one package, a threeband fluorescent lamp, a UV light LED+RGB phosphor, an organic EL lightsource and so on. However, Patent document 2 lacks concrete descriptionconcerning a RG phosphor that uses blue light as an excitation source.

On the other hand, a tetravalent manganese-activated fluoro-metalatephosphor is described, for example, in US20060169998A1 (Patent document3). However, Patent document 3 does not describe a combination with agreen phosphor of high efficiency and its high color gamut (NTSC ratio).

Patent document 1: Japanese Patent Laying-Open No. 2003-121838Patent document 2: Japanese Patent Laying-Open No. 2004-287323Patent document 3: US20060169998A1

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made to solve the above problem, and itis an object of the present invention to provide a light-emitting devicehaving excellent color gamut (NTSC ratio) by using a specific phosphorthat emits light at high efficiency with light ranging from 430 to 480nm from a light-emitting element.

Means for Solving the Problems

A light-emitting device according to the present invention is alight-emitting device including a light-emitting element emittingprimary light, and a light converter absorbing a part of the primarylight emitted from the light-emitting element and emitting secondarylight having a longer wavelength than the primary light, the lightconverter including a green light-emitting phosphor and a redlight-emitting phosphor,

the green light-emitting phosphor including at least one selected from:

-   -   a divalent europium-activated oxynitride phosphor which is        β-type SiAlON, substantially represented by a general formula        (A): Eu_(a)Si_(b)Al_(c)O_(d)N_(e) (in general formula (A),        0.005≦a≦0.4, b+c=12, and d+e=16), and    -   a divalent europium-activated silicate phosphor substantially        represented by a general formula (B):        2(Ba_(1-f-g)MI_(f)Eu_(g))O.SiO₂ (in general formula (B), MI        represents at least one alkaline earth metal element selected        from Mg, Ca and Sr, 0<f≦0.55, and 0.03≦g≦0.10),

the red light-emitting phosphor including at least one selected from:

-   -   a tetravalent manganese-activated fluoro-tetravalent metalate        phosphor substantially represented by a general formula (C):        MII₂(MIII_(1-h)Mn_(h))F₆ (in general formula (C), MII represents        at least one alkaline metal element selected from Li, Na, K, Rb        and Cs, MITI represents at least one tetravalent metal element        selected from Ge, Si, Sn, Ti and Zr, and 0.001≦h≦0.1), and    -   a tetravalent manganese-activated fluoro-tetravalent metalate        phosphor substantially represented by a general formula (D):        MIV(MIII_(1-h)Mn_(h))F₆ (in general formula (D), MIV represents        at least one alkaline earth metal element selected from Mg, Ca,        Sr, Ba and Zn, MIII represents at least one tetravalent metal        element selected from Ge, Si, Sn, Ti and Zr, and 0.001≦h≦0.1).

It is here preferable that MII is K and MIII is Ti.

In the light-emitting device according to the present invention, it ispreferable that 0.005≦h≦0.05.

In the light-emitting device according to the present invention, MI ispreferably Sr.

In the light-emitting device according to the present invention, thelight-emitting element is preferably a gallium nitride-basedsemiconductor emitting primary light having a peak wavelength of 430 to480 nm.

Effects of the Invention

According to the present invention, there is provided a light-emittingdevice capable of obtaining white light having significantly excellentcolor gamut (NTSC ratio) while efficiently absorbing the light emittedfrom the light-emitting element in the light converter and emittinghighly efficient white light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view schematically showing a light-emittingdevice 1 of a preferred example of the present invention.

FIG. 2 is a graph showing a luminous spectrum distribution of oneconcrete example of a divalent europium-activated oxynitride greenlight-emitting phosphor which is a β-type SiAlON usable in alight-emitting device of the present invention.

FIG. 3 is a graph showing a luminous spectrum distribution of oneconcrete example of a divalent europium-activated silicate phosphorusable in a light-emitting device of the present invention.

FIG. 4 is a graph showing a luminous spectrum distribution of oneconcrete example of a tetravalent manganese-activated fluoro-tetravalentmetalate phosphor usable in a light-emitting device of the presentinvention.

FIG. 5 is a graph showing a luminous spectrum distribution of alight-emitting device which is one preferred example of the presentinvention.

FIG. 6 is a chromaticity diagram showing color gamut of a LCDincorporating a light-emitting device which is one preferred example ofthe present invention as a backlight light source.

FIG. 7 is a graph showing a luminous spectrum distribution of aconventional light-emitting device using a yellow light-emittingphosphor.

FIG. 8 is a chromaticity diagram showing color gamut of a LCDincorporating a conventional light-emitting device using a yellowlight-emitting phosphor as a backlight light source.

DESCRIPTION OF THE REFERENCE SIGNS

1 light-emitting device, 2 light-emitting element, 3 light converter, 4green light-emitting phosphor, 5 red light-emitting phosphor, 6 sealant

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 is a section view schematically showing a light-emitting device 1of a preferred example of the present invention. As shown in FIG. 1,light-emitting device 1 of the present invention basically includes alight-emitting element 2 emitting primary light, and a light converter 3absorbing a part of the primary light emitted from light-emittingelement 2 and emitting secondary light having a wavelength longer thanthat of the primary light, and light converter 3 includes a greenlight-emitting phosphor 4 and a red light-emitting phosphor 5. FIG. 1illustrates an example wherein light-emitting element 2, greenlight-emitting phosphor 4 and red light-emitting phosphor 5 are sealedin a sealant 6, so that light converter 3 is realized to be able toabsorb a part of the primary light emitted from light-emitting element 2and emit secondary light having a wavelength longer than that of theprimary light. Light converter 3 in light-emitting device 1 of thepresent invention includes, as green light-emitting phosphor 4, at leastone selected from the following (A) a divalent europium-activatedoxynitride phosphor which is β-type SiAlON and (B) a divalenteuropium-activated silicate phosphor, and includes, as a redlight-emitting phosphor, at least one selected from the following two(C) and (D) tetravalent manganese-activated fluoro-tetravalent metalatephosphors.

(A) Divalent Europium-Activated Oxynitride Green Light-Emitting Phosphorwhich is β-Type SiAlON

The divalent europium-activated oxynitride green light-emitting phosphoris substantially represented by:

Eu_(a)Si_(b)Al_(c)O_(d)N_(e)  general formula (A):

(hereinafter, the divalent europium-activated oxynitride greenlight-emitting phosphor is referred to as “first green light-emittingphosphor”). In general formula (A), Eu represents europium, Sirepresents silicon, Al represents aluminum, O represents oxygen, and Nrepresents nitrogen. In general formula (A), a value of “a” representinga composition ratio (concentration) of Eu is 0.005≦a≦0.4. When the valueof “a” is less than 0.005, sufficient brightness is not obtained,whereas when the value of “a” exceeds 0.4, brightness largely decreasesdue to concentration quenching or the like. From the viewpoints ofstability of powder characteristics and uniformity of matrix, the valueof “a” in the above formula is preferably 0.01≦a≦0.2. in general formula(A), “b” that represents a composition ratio (concentration) of Si and“c” that represents a composition ratio (concentration) of Al satisfyb+c=12, and “d” that represents a composition ratio (concentration) of Oand “e” that represents a composition ratio (concentration) of N satisfyd+e=16.

Concrete examples of the first green light-emitting phosphor include,but are not limited to, Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95),Eu_(0.10)Si_(11.00)Al_(1.00)O_(0.10)N_(15.90),Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70),Eu_(0.15)Si_(10.00)Al_(2.00)O_(0.20)N_(15.80),Eu_(0.01)Si_(11.60)Al_(0.40)O_(0.01)N_(15.99), andEu_(0.005)Si_(11.70)Al_(0.30)O_(0.03)N_(15.97).

(B) Divalent Europium-Activated Silicate Phosphor

The divalent europium-activated silicate phosphor is substantiallyrepresented by:

2(Ba_(1-f-g)MI_(f)Eu_(g))O.SiO₂  general formula (B):

(hereinafter, the divalent europium-activated silicate phosphor isreferred to as “second green light-emitting phosphor”). In generalformula (B), Ba represents barium, Eu represents europium, O representsoxygen, and Si represents silicon. In general formula (B), MI representsat least one alkaline earth metal element selected from Mg, Ca and Sr,and for obtaining highly efficient matrix, MI is preferably Sr. Ingeneral formula (B), “f” that represents a composition ratio(concentration) of MI is 0≦f≦0.55, and the value of “f” falling withinthis range makes it possible to obtain green light emission ranging from510 to 540 nm. When the value of “f” exceeds 0.55, the green lightemission is yellowish, and color purity is impaired. Further, from theviewpoints of efficiency and color purity, the value of “f” ispreferably within the range of 0.015≦f≦0.45. A value of “g” thatrepresents a composition ratio (concentration) of Eu in general formula(B) is 0.03≦g≦0.10. This is because when the value of “g” is less than0.03, sufficient brightness is not obtained, and when the value of “g”exceeds 0.10, the brightness greatly decreases due to concentrationquenching or the like. From the viewpoints of brightness and stabilityof powder characteristics, the value of “g” preferably falls within therange of 0.04≦g≦0.08.

Concrete examples of the second green light-emitting phosphor include,but are not limited to, 2(Ba_(0.70)Sr_(0.26)Eu_(0.04)).SiO₂,2(Ba_(0.57)Sr_(0.38)Eu_(0.05))O.SiO₂,2(Ba_(0.53)Sr_(0.43)Eu_(0.04))O.SiO₂,2(Ba_(0.82)Sr_(0.15)Eu_(0.03))O.SiO₂,2(Ba_(0.46)Sr_(0.49)Eu_(0.05))O.SiO₂,2(Ba_(0.59)Sr_(0.35)Eu_(0.06))O.SiO₂,2(Ba_(0.52)Sr_(0.40)Eu_(0.08))O.SiO₂,2(Ba_(0.85)Sr_(0.10)Eu_(0.05))O.SiO₂,2(Ba_(0.47)Sr_(0.50)Eu_(0.03))O.SiO₂,2(Ba_(0.54)Sr_(0.36)Eu_(0.10))O.SiO₂,2(Ba_(0.69)Sr_(0.25)Ca_(0.02)Eu_(0.04))O.SiO₂,2(Ba_(0.56)Sr_(0.38)Mg_(0.01)Eu_(0.05))O.SiO₂, and2(Ba_(0.81)Sr_(0.13)Mg_(0.01)Ca_(0.01)Eu_(0.04))O.SiO₂.

(C) Tetravalent Manganese-Activated Fluoro-Tetravalent Metalate Phosphor

The tetravalent manganese-activated fluoro-tetravalent metalate phosphoris substantially represented by:

MII₂(MIII_(1-h)Mn_(h))F₆  general formula (C):

(hereinafter, the tetravalent manganese-activated fluoro-tetravalentmetalate phosphor is referred to as “first red light-emittingphosphor”). In general formula (C), Mn represents manganese, and Frepresents fluorine. In general formula (C), MII represents at least onealkaline metal element selected from Na, K, Rb and Cs, and from theviewpoints of brightness and stability of powder characteristics, MII ispreferably K. In general formula (C), MIII represents at least onetetravalent metal element selected from Ge, Si, Sn, Ti and Zr, and fromthe viewpoints of brightness and stability of powder characteristics,MIII is preferably Ti. In general formula (C), a value of “h” thatrepresents a composition ratio (concentration) of Mn is 0.001≦h≦0.1.This is because when the value of “h” is less than 0.001, a problemarises that sufficient brightness is not obtained, whereas when a valueof “h” exceeds 0.1, a problem arises that the brightness greatlydecreases due to concentration quenching or the like. From theviewpoints of brightness and stability of powder characteristics, thevalue of “h” is preferably 0.005≦h≦0.5.

Concrete examples of the first red light-emitting phosphor include, butare not limited to, K₂(Ti_(0.99)Mn_(0.01))F₆, K₂(Ti_(0.9)Mn_(0.1))F₆,K₂(Ti_(0.999)Mn_(0.001))F₆, Na₂(Zr_(0.98)Mn_(0.02))F₆,Cs₂(Si_(0.95)Mn_(0.05))F₆, Cs₂(Sn_(0.98)Mn_(0.02))F₆,K₂(Ti_(0.88)Zr_(0.10)Mn_(0.02))F₆, Na₂(Ti_(0.75)Sn_(0.20)Mn_(0.05))F₆,Cs₂(Ge_(0.999)Mn_(0.001))F₆, and(K_(0.80)N_(0.20))₂(Ti_(0.69)Ge_(0.30)Mn_(0.01))F₆.

(D) Tetravalent Manganese-Activated Fluoro-Tetravalent Metalate Phosphor

The tetravalent manganese-activated fluoro-tetravalent metalate phosphoris substantially represented by:

MIV(MIII_(1-h)Mn_(h))F₆  general formula (D):

(hereinafter, the tetravalent manganese-activated fluoro-tetravalentmetalate phosphor is referred to “second red light-emitting phosphor”).In general formula (D), Mn represents manganese, and F representsfluorine. In general formula (D), MIII represents, likewise the MIII ingeneral formula (C), at least one tetravalent metal element selectedfrom Ge, Si, Sn, Ti and Zr, and from the same reason, MIII is preferablyTi. In general formula (D), MIV represents at least one alkaline earthmetal element selected from Mg, Ca, Sr, Ba and Zn, and from theviewpoints of brightness and stability of powder characteristics, MIV ispreferably Ca. In general formula (D), a value of “h” that represents acomposition ratio (concentration) of Mn is, likewise the “h” in generalformula (C), 0.001≦h≦0.1, and is preferably 0.005≦h≦0.5 from the samereason.

Concrete examples of the second red light-emitting phosphor include, butare not limited to, Zn(Ti_(0.98)Mn_(0.02))F₆,Ba(Zr_(0.995)Mn_(0.005))F₆, Ca(Ti_(0.995)Mn_(0.005))F₆, andSr(Zr_(0.98)Mn_(0.02))F₆.

The light converter in the light-emitting device of the presentinvention includes, as a green light-emitting phosphor, at least oneselected from (A) divalent europium-activated oxynitride phosphor (firstgreen light-emitting phosphor) which is β-type SiAlON and (B) divalenteuropium-activated silicate phosphor (second green light-emittingphosphor), and includes, as a red light-emitting phosphor, at least oneselected from two kinds of (C) tetravalent manganese-activatedfluoro-tetravalent metalate phosphor (first red light-emitting phosphor)and (D) tetravalent manganese-activated fluoro-tetravalent metalatephosphor (second red light-emitting phosphor). FIG. 2 shows a luminousspectrum distribution of a concrete example of a divalenteuropium-activated oxynitride green light-emitting phosphor which is aβ-type SiAlON (concrete composition:Eu_(0.05)Se_(11.50)Al_(0.50)O_(0.05)N_(15.95)) usable in alight-emitting device of the present invention, FIG. 3 shows a luminousspectrum distribution of a concrete example of a divalenteuropium-activated silicate phosphor (concrete composition:2(Ba_(0.70)Sr_(0.26)Eu_(0.04))O.SiO₂) usable in a light-emitting deviceof the present invention, and FIG. 4 shows a luminous spectrumdistribution of a concrete example of a tetravalent manganese-activatedfluoro-tetravalent metalate phosphor (concrete composition:K₂(Ti_(0.99)Mn_(0.01))F₆) usable in a light-emitting device of thepresent invention. Any luminous spectrums shown in FIG. 2 to FIG. 4 areresults measured by using a fluorescent spectrophotometer at anexcitation wavelength of 450 nm, and the vertical axis represents anintensity (arbitrary unit), and the horizontal axis represents awavelength (nm).

In the light-emitting device of the present invention, a mixing ratiobetween the green light-emitting phosphor and the red light-emittingphosphor is not particularly limited, however, the green light-emittingphosphor is mixed preferably within the range of 5 to 70% by weightratio, and more preferably within the range of 15 to 45% by weightratio, relative to the red light-emitting phosphor.

FIG. 5 is a graph showing a luminous spectrum distribution of alight-emitting device of one preferred example of the present invention(light-emitting device fabricated in Example 1 as described later), andin FIG. 5, the vertical axis represents an intensity (arbitrary unit),and the horizontal axis represents a wavelength (nm). FIG. 6 is achromaticity diagram (CIE 1931) showing color gamut of a LCDincorporating a light-emitting device of one preferred example of thepresent invention (light-emitting device fabricated in Example 1 asdescribed later) as a backlight light source. On the other hand, FIG. 7is a graph showing a luminous spectrum distribution of a conventionallight-emitting device using a yellow light-emitting phosphor(light-emitting device fabricated in Comparative example 1 as describedlater), and FIG. 8 is a chromaticity diagram (CIE 1931) showing colorgamut of a LCD incorporating the light-emitting device as a backlightlight source. The luminous spectrum distribution of the light-emittingdevice shown in FIG. 5 and FIG. 7 is a result measured by usingMCPD-2000 (available from OTSUKA ELECTRONICS CO., LTD.), and the colorgamut shown in FIG. 6 and FIG. 8 is a result measured by using Bm5(available from TOPCON CORPORATION). The results of FIG. 5 to FIG. 8demonstrate that unlike the conventional light-emitting device, thelight-emitting device of the present invention provides a light-emittingdevice capable of obtaining white light exhibiting significantlyexcellent color gamut (NTSC ratio) while efficiently absorbing lightemitted from the light-emitting element in the light converter, andemitting highly efficient white light. NTSC ratio is a percentagerelative to an area of triangle obtained by connecting chromaticitycoordinates of red, green and blue, namely chromaticity coordinates (x,y) of red (0.670, 0.330), green (0.210, 0.710), and blue (0.140, 0.080)in a XYZ color system chromaticity diagram of red, green and bluedefined by NTSC (National Television System Committee).

While the light-emitting element used in the light-emitting device ofthe present invention as described above is not particularly limited, agallium nitride (GaN)-based semiconductor emitting primary light of theblue region having a peak wavelength ranging from 430 to 480 nm (morepreferably 440 to 480 nm) is preferably used as a light-emittingelement. When a light-emitting element having a peak wavelength of lessthan 430 nm is used, color rendering property is impaired because ofdecreased contribution of a blue light component, and practicality maybe impaired. When a light-emitting element having a peak wavelengthexceeding 480 nm is used, brightness in white decreases, so thatpracticality may be impaired.

Other configuration of the light-emitting device of the presentinvention is not particularly limited as far as the aforementionedfeatures are realized. As sealant 6, a resin material havingtranslucency, such as an epoxy resin, a silicone resin, and a urearesin, may be used unlimitatively. Of course, light converter 3 maycontain an appropriate additive such as SiO₂, TiO₂, ZrO₂, Al₂O₃, andY₂O₃ in addition to the phosphor and the sealant as far as the effect ofthe present invention is not hindered.

The green light-emitting phosphor and the red light-emitting phosphorfor use in the light-emitting device of the present invention asdescribed above are well known in the art, and may be produced by aconventionally known appropriate method, or are available as acommercial product.

In the following, the present invention will be more specificallydescribed by way of Examples and Comparative examples, however, thepresent invention will not be limited thereto.

Example 1

Light-emitting device 1 of the example shown in FIG. 1 was fabricated inthe following manner. As light-emitting element 2, a gallium nitride(GaN)-based semiconductor having a peak wavelength at 450 nm was used,and in light converter 3, Eu_(0.05)Si_(11.50)Al_(0.50)O_(0.05)N_(15.95)(β-type SiAlON) was used as a green light-emitting phosphor, andK₂(Ti_(0.99)Mn_(0.01))F₆ was used as a red light-emitting phosphor. A30:70 (weight ratio) mixture of these green light-emitting phosphor andred light-emitting phosphor was dispersed in a predetermined resin(ratio between a resin and a phosphor was 1.00:0.25) to fabricate alight converter. In this manner, a light-emitting device of Example 1was fabricated.

Comparative Example 1

A light-emitting device was fabricated in a similar manner as Example 1except that a yellow light-emitting phosphor represented by(Y_(0.40)Gd_(0.45)Ce_(0.15))₃Al₅O₁₂ was used in a light converter.

For the light-emitting devices obtained respectively in Example 1, andComparative example 1, brightness, Tc-duv and color gamut (NTSC ratio)were evaluated. Brightness was determined by illuminating in a conditionof a forward current (IF) of 20 mA, and converting white light from thelight-emitting device into photocurrent. A value of Tc-duv wasdetermined by illuminating in a condition of a forward current (IF) of20 mA, measuring white light from the light-emitting device withMCPD-2000 (available from OTSUKA ELECTRONICS CO., LTD.). A value ofcolor gamut (NTSC ratio) was determined by incorporating the fabricatedlight-emitting device as a backlight light source of a commerciallyavailable LCD TV display, and measuring by Bm5 available from TOPCONCORPORATION. The results are shown in Table 1.

TABLE 1 Brightness Color gamut (relative value) Tc-duv (NTSC ratio)Example 1 96.5% 8700K + 0.002 88.3% Comparative 100.0% 8700K + 0.00270.1% example 1

Table 1 demonstrates that the light-emitting device of the presentinvention exhibits tremendously improved color gamut (NTSC ratio)compared with the conventional one, and has preferable characteristicsas a backlight for a medium- or small-sized LCD.

Example 2

A light-emitting device was fabricated in a similar manner as Example 1except that a gallium nitride (GaN)-based semiconductor having a peakwavelength at 440 nm was used as light-emitting element 2,2(Ba_(0.70)Sr_(0.26)Eu_(0.04))O.SiO₂ was used as a green light-emittingphosphor, and K₂(Ti_(0.995)Mn_(0.005))F₆ was used as a redlight-emitting phosphor.

Comparative Example 2

A light-emitting device was fabricated in a similar manner as Example 2except that a yellow light-emitting phosphor represented by(Y_(0.40)Gd_(0.50)Ce_(0.10))₃Al₅O₁₂ was used in a light converter.

For the light-emitting devices obtained in Example 2 and Comparativeexample 2, brightness, Tc-duv and color gamut (NTSC ratio) wereevaluated in a similar manner as the cases of the light-emitting devicesof Example 1 and Comparative example 1 as described above. The resultsare shown in Table 2.

TABLE 2 Brightness Color gamut (relative value) Tc-duv (NTSC ratio)Example 2 96.1% 7900K + 0.002 88.1% Comparative 100.0% 7900K + 0.00269.8% example 2

Table 2 demonstrates that the light-emitting device of the presentinvention exhibits tremendously improved color gamut (NTSC ratio)compared with the conventional one, and has preferable characteristicsas a backlight for a medium- or small-sized LCD.

Examples 3 to 8, Comparative Examples 3 to 8

Light-emitting devices of Examples 3 to 8 and Comparative examples 3 to8 were fabricated in a similar manner as Example 1 except thatcombinations of a peak wavelength of a light-emitting element andphosphors as shown in the following Table 3 were used respectively, andbrightness, Tc-duv and color gamut (NTSC ratio) were evaluated in asimilar manner as described above. Results are also shown in Table 3.

TABLE 3 Light-emitting Brightness Color gamut element Phosphor (relativevalue) Tc-duv (NTSC ratio) Example 3 430 nm Green:Eu_(0.30)Si_(9.80)Al_(2.20)O_(0.30)N_(15.70) 96.6% 9500K + 0.001 86.4%Red: Na₂(Ti_(0.895)Zr_(0.100)Mn_(0.005))F₆ Comparative 430 nm Yellow:2(Sr_(0.92)Ba_(0.06)Eu_(0.02))O•SiO₂ 100.0% 9500K + 0.001 67.4% example3 Example 4 480 nm Green: Eu_(0.15)Si_(10.00)Al_(2.00)O_(0.20)N_(15.80)96.0% 8800K + 0.001 87.9% Red: Cs₂(Ti_(0.79)Si_(0.20)Mn_(0.01))F₆Comparative 480 nm Yellow: (Y_(0.40)Gd_(0.40)Ce_(0.20))₃Al₅O₁₂ 100.0%8800K + 0.001 70.0% example 4 Example 5 455 nm Green:2(Ba_(0.82)Sr_(0.15)Eu_(0.03))O•SiO₂ 96.4% 8900K + 0.002 88.0% Red:Cs₂(Ti_(0.79)Si_(0.20)Mn_(0.01))F₆ Comparative 455 nm Yellow:(Y_(0.40)Gd_(0.45)Ce_(0.15))₃Al₅O₁₂ 100.0% 8900K + 0.002 70.0% example 5Example 6 460 nm Green: Eu_(0.01)Si_(11.60)Al_(0.40)O_(0.01)N_(15.99)96.5% 6800K + 0.002 87.8% Red: Ba(Ti_(0.99)Mn_(0.01))F₆ Comparative 460nm Yellow: (Y_(0.45)Gd_(0.45)Ce_(0.10))₃Al₅O₁₂ 100.0% 6800K + 0.00270.3% example 6 Example 7 445 nm Green:2(Ba_(0.85)Sr_(0.10)Eu_(0.05))O•SiO₂ 96.5% 6800K + 0.002 88.5% Red:(K_(0.80)Na_(0.20))₂(Ti_(0.69)Ge_(0.30)Mn_(0.01))F₆ Comparative 445 nmYellow: (Y_(0.35)Gd_(0.45)Ce_(0.20))₃Al₅O₁₂ 100.0% 6800K + 0.002 70.4%example 7 Example 8 470 nm Green:Eu_(0.005)Si_(11.70)Al_(0.30)O_(0.03)N_(15.97) 96.3% 9000K + 0.001 88.4%Red: Zn(Ti_(0.849)Sn_(0.150)Mn_(0.001))F₆ Comparative 470 nm Yellow:(Y_(0.40)Gd_(0.45)Ce_(0.15))₃Al₅O₁₂ 100.0% 9000K + 0.001 70.2% example 8

Also Table 3 demonstrates that the light-emitting device of the presentinvention exhibits tremendously improved color gamut (NTSC ratio)compared with the conventional one, and has desired characteristics as abacklight for a medium- or small-sized LCD.

1. A light-emitting device comprising a light-emitting element that is agallium nitride-based semiconductor emitting primary light having a peakwavelength of 430 to 480 nm, and a light converter including a firstphosphor absorbing a part of the primary light emitted from thelight-emitting element and emitting secondary light having a longerwavelength than the primary light, and a second phosphor emittingsecondary light having a longer wavelength than the secondary lightemitted from the first phosphor, wherein said the second phosphor is atetravalent manganese⁻activated fluoro-tetravalent metalate phosphorsubstantially represented by a general formula (C):MII₂(MIII_(1-h)Mn_(h))F₆ (in said general formula (C), MII represents atleast one alkaline metal element selected from Li, Na, K, Rb and Cs,MIII represents at least one tetravalent metal element selected from Ge,Si, Sn, Ti and Zr, and 0.001≦h≦0.1), and wherein a mixing ratio of thesecond phosphor is higher than that of the first phosphor.
 2. Thelight-emitting device according to claim 1, wherein the light convertercontains at least one additive selected from the group of SiO₂, TiO₂,ZrO₂, Al₂O₃ and Y₂O₃.
 3. The light⁻emitting device according to claim 1,wherein MIII is at least one selected from the group of Si and Ti. 4.The light-emitting device according to claim 1, wherein 0.005≦h≦0.05.